Signal choppers are generally known and are typically used to either block an incident signal or change one or more characteristics of the incident signal so that its exit form is different than its entry form. One of many applications for choppers is for use in imaging systems. A typical imaging system includes a detector for detecting an incident signal produced by or reflected from a source. A chopper may be disposed between the incident signal and the detector to interrupt the signal before it reaches the detector.
Electrical choppers are generally known and have been used in imaging systems. One problem with electrical choppers, however, is that they cannot be used with thermal imaging systems because the thermal detector needs a thermal reference to provide successful chopping. Another problem with electrical choppers is the need for complex electronic circuitry in order to achieve chopping.
Thermal choppers are also generally known and are typically used in thermal imaging systems. The thermal chopper provides an intermediate object between a scene, which is the source of the signal, and the detector. In the thermal imaging system, the chopper provides a thermal reference for a thermal detector. Therefore, with respect to the portion of the signal being chopped the detector detects the thermal reference as opposed to the incident signal.